1. Field of the Invention
The present invention relates generally to power supplies, and more specifically to a feedback method and apparatus for adaptively controlling power supplied to a hot-pluggable subsystem.
2. Background of the Invention
Computers and other electronic systems such as telecom systems require replacement and/or addition of subsystems without removing power from a host system. Known as xe2x80x9chot-pluggablexe2x80x9d subsystems, these electrical devices must operate properly after connection and disconnection, while not disrupting the operation of other electronic circuits. Telecom systems typically operate at a much higher voltage (xe2x88x9248V) and telecom subsystems typically have high current drains due to the low-impedance nature of telephony circuits. Thus, the input capacitances required to filter EMI and conducted ripple on the input of telecom subsystems are typically large and a hot-pluggable subsystem for telecom generally requires sophisticated inrush current protection.
Additionally, peripheral devices, storage devices and redundant processor modules in both network server systems and personal computing systems can be removed or attached while the systems remain active. Network connections between systems must also support active connection and disconnection, since the entire network should not be shut down to add or remove computers or other devices. Power to connected sub-systems may be supplied through network interface cables. For example, the Powered Ethernet Specification 802.3 promulgated by the Institute of Electrical and Electronic Engineers (IEEE), specifies an interface wherein power is supplied through the network cable connection. Hot-pluggable network hubs, network telecom cards including fiber optic interfaces, transceivers and cards for analog telephonic interfaces may all be powered by a host system.
Inrush current must be managed in hot-plugging systems, as the transients generated when the hot-pluggable subsystem is connected to the host system can damage connectors, cause dips in the power supply rails and generate electromagnetic interference (EMI) that affect the operation of the host system and other connected subsystems.
Power supplies for hot-pluggable subsystems having a minimum of electrical connections and incorporated within small integrated circuit packages are very desirable. In general it is useful to provide power supply integrated circuits requiring a minimum of circuit area and external connections.
Power supplies for a hot-pluggable subsystem are typically required to provide a stable time period in which the power supply voltage applied to the hot-pluggable device does not vary while the hot-pluggable device initializes. This presents difficulty in that mechanical contact bounce may electrically connect and disconnect the power supply conductors several times before the device is properly coupled. A de-bounce time interval and/or a power-on-reset (POR) time interval are typically provided to prevent improperly initializing a hot-pluggable subsystem, but implementation of the de-bounce and power-on-reset time intervals typically requires additional components, adding to size, complexity and cost of power supply electronics.
Other features desirable in a power supply for coupling to a hot-pluggable sub-system are short-circuit protection (or current limiting) to prevent misalignment or accidental shorting of the power supply pins from damaging the power supply or hot-pluggable subsystem. Short-circuit protection differs from inrush current protection in that short-circuit protection must distinguish from a transient short-circuit type load (virtual AC short circuit) that is produced by the large input capacitors of hot-pluggable subsystem power supplies or bypass capacitors. The pass device used in a hot-pluggable power supply can fail or be degraded in operating characteristics and reliability if a short circuit is placed across the output terminals of a hot-pluggable power supply.
Typically, implementation of short-circuit discrimination vs. current limiting requires additional complexity within the power supply control circuits and additional components to set operating levels, etc. Large capacitors are required to prevent startup transients from turning on the pass device through the parasitic capacitances of the pass device. Short-circuit protection circuits as well as current limiting circuits are generally desirable with an auto-restart feature so that input power does not have to be removed in order for the hot-pluggable power supply to recover from the protection conditions. Auto-restart circuits typically require external timing components, and due to the long time constants required, these restart circuits use large capacitors.
Under-voltage lockout (UVLO) protection is also desirable in hot-pluggable systems, so that the hot-pluggable sub-system power supply does not produce an output until the power supply input has reached a minimum voltage level. Over-voltage protection (OVP) is also desirable, to prevent damage to the hot-pluggable subsystems power converters and other components.
Therefore, it would be desirable to provide an improved method and system for controlling the current supplied to a hot-pluggable subsystem. It would be further desirable to control power supply current during initialization and mechanical contact bounces while minimizing additional timing components, external connections and external components to support operational features.
It would additionally be desirable to incorporate UVLO protection, OVP and short-circuit protection without requiring additional external connections. It would further be desirable to provide the above-mentioned features within a small integrated circuit package having a minimum of electrical connections.
The above objective of adaptively controlling power supplied to a hot-pluggable subsystem is achieved in a feedback method and apparatus. The apparatus includes a pass device for controlling a power supply output and a control circuit coupled to a control terminal of the pass device. The control circuit controls a rate of rise of a control signal at the control terminal of the pass device during turn-on of the pass device in conformity with a detected current through the pass transistor. A capacitor used to prevent transient turn-on of the pass device may be subsequently used for timing purposes by isolating the capacitor with an isolation circuit. Sequencing of timed events may be programmed by multiple impedances connected external to an integrated circuit embodying the apparatus to set multiple time constants for the timing function.
The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.